A significant challenge to fielding custom earplugs is the process for measuring the ears of each user. Like getting measured for custom fitting clothing, customers have to be measured for custom fitting earplugs. That measurement is traditionally accomplished by taking a physical ear impression.
The process of taking a physical ear impression involves injecting a liquid silicone material into the ear to completely fill the ear canal. The liquid silicone flows into and conforms to the exact shape of the ear canal before curing into a flexible solid part. Once fully cured, the solid part is removed from the ear and termed the ear impression. Because it was formed in direct contact with the skin, the surface of the ear impression shows the exact contours of the skin of the ear canal.
The traditional process for earplug fabrication is initiated directly from the physical ear impression. Skilled craftspersons trim and apply wax directly to the silicone ear impression to form it into to the desired earplug shape. Next, the modified impression serves as a master from which a new mold is built and the earplug product is cast from that mold. Newly minted earplug products are later hand-ground and polished to get their final shape. This process is manual labor intensive and difficult to control precisely since each operation is completed by hand working directly on the original record of the ear's shape, the ear impression. If there are any mistakes those errors are difficult to identify and correct because one cannot readily compare the final resulting earplug to the original unmodified ear impression. Also, if there are major mistakes, such as inadvertently trimming away too much of the original ear impression, the process has to be started over.
In recent years industry leaders have developed methods for fabricating custom earplugs using digital manufacturing processes. Most digital processes have used laser scanning equipment to create a digital map of the ear impression surface (a “digital earshape”). Since the impression surface matches the ear surface, a digital earshape is a record of the shape of the ear and serves as the basis for subsequent production operations. The digital earshape can be manipulated using various computerized software tools to form the earplug shape which is then rendered into a physical object through a combination of computer controlled rapid prototyping techniques and injection molding operations.
Physical ear impressions do not provide information about anatomical features below the surface of the ear canal skin (sub-dermal features) such as the thickness of soft tissues or the precise locations along the ear canal that are backed by inflexible bone. Since the ear impression is simply a cast made using the ear canal as a mold, the ear impression cannot reveal anatomical information beyond the characteristics of the skin with which it was in contact while it cured. Below-surface information in not available from the cast of a surface feature or from a scan of such a cast.
A typical earplug manufacturing process utilizes data acquire from physical ear impressions. However, because physical ear impressions do not provide anatomical information, the earplug manufacturing process cannot utilize anatomical information relating to sub-dermal structures within the ear, as for example, the precise location of the temporal bone and the thickness of soft tissue layers, on a user specific basis as a parameter in determining the shape of a hearing protector earplug.
Although some current processes claim to build hearing aids that fit to the “bony part” of the ear, these processes assume the bony part to be the region at, around, or deeper than the “second bend.” The qualitative terms “first bend” and “second bend” are common in the ear insert industry. Although it is widely held and qualitatively true that the ear canal enters the temporal bone near the ear canal's second bend, there has not been a precise means of defining or identifying the second bend or defining where the bony part begins relative to that second bend across individuals. For building high-performance ear insert devices, knowing only the qualitative approximate location of the bony part is insufficient and may result in ear insert devices that are too long or too large near the bone and are therefore too uncomfortable to wear. Similarly, ear insert devices built conservatively to stay clear of the second bend may not perform at acceptable levels.